added concurrent read invariant test

main/filesystem-invariants-tests/src/test/java/org/cryptomator/filesystem/invariants/FileReadWriteTests.java

@@ -4,13 +4,23 @@ import static org.cryptomator.filesystem.invariants.matchers.NodeMatchers.hasCon
 import static org.hamcrest.CoreMatchers.containsString;
 import static org.hamcrest.CoreMatchers.is;
 import static org.hamcrest.CoreMatchers.not;
+import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertThat;
+import static org.junit.Assert.assertTrue;
 import static org.junit.Assume.assumeThat;
 
 import java.nio.ByteBuffer;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Future;
+import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
 
 import org.cryptomator.filesystem.File;
 import org.cryptomator.filesystem.FileSystem;
+import org.cryptomator.filesystem.ReadableFile;
 import org.cryptomator.filesystem.WritableFile;
 import org.cryptomator.filesystem.invariants.FileSystemFactories.FileSystemFactory;
 import org.cryptomator.filesystem.invariants.WaysToObtainAFile.WayToObtainAFile;
@@ -130,4 +140,58 @@ public class FileReadWriteTests {
 		assertThat(file, hasContent(expectedData));
 	}
 
+	@Theory
+	public void testConcurrentPartialReadsDontInterfere(FileSystemFactory fileSystemFactory, WayToObtainAFile wayToObtainAnExistingFile) throws InterruptedException, ExecutionException {
+		assumeThat(wayToObtainAnExistingFile.returnedFilesExist(), is(true));
+
+		FileSystem fileSystem = fileSystemFactory.create();
+		byte[] originalData = new byte[] {32, 44, 1, -3, 4, 66, 4};
+		byte[] expectedData1 = new byte[] {-3, 4, 66};
+		byte[] expectedData2 = new byte[] {44, 1, -3, 4};
+		File file = wayToObtainAnExistingFile.fileWithNameAndContent(fileSystem, FILE_NAME, originalData);
+
+		// control flag to make sure thread timing is synchronized correctly
+		AtomicInteger state = new AtomicInteger();
+
+		// set position, then wait before read:
+		byte[] actualData1 = new byte[3];
+		Callable<?> readTask1 = () -> {
+			try (ReadableFile readable = file.openReadable()) {
+				ByteBuffer buf = ByteBuffer.wrap(actualData1);
+				readable.position(3);
+				assertTrue("readTask1 must be the first to set its position", state.compareAndSet(0, 1));
+				Thread.sleep(20);
+				assertTrue("readTask1 must be the last to actually read data", state.compareAndSet(3, 4));
+				readable.read(buf);
+				return null;
+			}
+		};
+
+		// wait, then set position and read:
+		byte[] actualData2 = new byte[4];
+		Callable<?> readTask2 = () -> {
+			try (ReadableFile readable = file.openReadable()) {
+				ByteBuffer buf = ByteBuffer.wrap(actualData2);
+				Thread.sleep(10);
+				readable.position(1);
+				assertTrue("readTask2 must be second to set its position", state.compareAndSet(1, 2));
+				readable.read(buf);
+				assertTrue("readTask2 must be first to finish reading", state.compareAndSet(2, 3));
+				return null;
+			}
+		};
+
+		// start both read tasks at the same time:
+		ThreadPoolExecutor executor = new ThreadPoolExecutor(2, 2, 0, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());
+		executor.prestartAllCoreThreads();
+		Future<?> task1Completed = executor.submit(readTask1);
+		Future<?> task2Completed = executor.submit(readTask2);
+		task1Completed.get();
+		task2Completed.get();
+		executor.shutdown();
+
+		assertArrayEquals(expectedData1, actualData1);
+		assertArrayEquals(expectedData2, actualData2);
+	}
+
 }